Just pay people for the value they provide. I think there's some room to argue that a remote only employee provides less value. Everyone in the same timezone, lack of face to face time, hallway encounters, going out to lunch, etc. have tangible value to the employer that is lost in the transition to remote work. But the arguments I see from Facebook and in this article are about cost of living. That's wrong. Price it based on value created by the employee.
If the permanence of remote work indeed turns into a long term trend, I think we're going to see some bumpy road ahead while individuals grapple with first moving and then local supply and demand in their new location. Fix your location, and then consider that if given the same pay, and same work, would you rather work remotely or in person? I would rather work in person for a couple of reasons including socialization, removal of distractions in a workplace environment, etc.